Just askin'. I think due to fandom discourse in recent years, the word 'filler' has earned a lot of undeserved negative connotations-- I mean, if the average fan calls an episode/arc/subplot filler, chances are they mean it as an insult, not a neutral observation. =/
But I think filler IS a neutral concept...the point is just to pad out the story with extra stuff, right? Which isn't always a bad thing. Sometimes you need those lower-stakes moments for pacing purposes, or to teach the viewer how the world of the story works, and how the characters live.
You could just mention those kinds of things in passing while they're prepping for a monster fight or sthg, but sometimes you want it to be more natural, y'know? Sometimes you want a calmer moment to play around with their personalities; to just have a little fun.
That being said, I don't actually like to use much filler. ^^; I'm just too impatient; I got too much going on to spend time making characters do inconsequential things just for the heck of it. My calm moments are always interwoven with exposition, and vice versa. You might say I'm an economical writer-- I pack as much information as possible into every inch of story, so we can get to the fun parts relatively quickly. :9
When I do write filler, though, it's usually comedic. As I always say, I am a drama writer by nature; I like to kill people and make them suffer~. And the opposite of that is actually letting them joke around and not worry about things for a change, so that's what I do when the plot takes a break.
Either that, or I do a short angst-solving arc...this is a technique I use in practically all my stories.
So we've either just finished a heavy moment, or we're going to be starting one soon but I need to buy some time to explain something first-- here's an opportunity to take one of these suffering characters and give them some emotional clarity in the B-plot.
"But that's just character development...does it really count as filler?" you might ask.
I dunno. Maybe not. ^^; But the way it plays out usually feels like filler, especially in comic scripts. I spend much more time letting the character muck around than actively working on their problem...the point is to create a situation where they can realize something about themselves at the end, even if it's something relatively small (or something that just seems small). Anything that makes them feel a little bit better, and more ready to handle whatever I throw at them next. ^^
Anyway, in all cases, I think the most crucial element to filler is 'fun'. You want the reader to enjoy it; you've got to craft it expressly for that purpose, or else they'll just be sitting there thinking 'ok so...when are we getting back to the plot??'
And while, as I said, I don't dislike filler as a concept, I absolutely despise it when writers forget that part. >_< About half of all the filler I've seen is either stuff created more for the writers to play with the characters and show off how funny they think they are than to give the audience anything interesting to watch...or just bland regurgitations of typical filler tropes ('beach episode', 'body swap/personality swap episode', 'what-the-characters-dream-about episode').
I guess if all you ever see is those things done badly, you could easily learn to hate all filler...I mean, it's understandable. =/ Fortunately, I'm not at that point, though.